Quadrature amplitude modulation (QAM) is a modulation scheme that conveys two signals by modulating the amplitudes of two carrier waves. The carrier waves, which are generally sinusoids, are known as quadrature carriers because they are out of phase with each other by 90 degrees. The modulate waves are then summed and transmitted to a destination. QAM is used extensively in the telecommunications field, and is increasingly being used in optical fiber systems.